Method for eliminating defects of electron beam selective melting printed ti-al alloy blade by hot isostatic pressing

Abstract

This invention provides a method for eliminating defects in TiAl alloy blades through electron beam selective melting printing, belonging to the field of hot isostatic pressing (HIP) of engine blades. After cleaning the blade blank, the method involves a three-step HIP process of purging air by circulating argon gas followed by heating and pressurization to complete the preparation of the TiAl alloy blade. During HIP, the blade is fitted into a fixture to prevent deformation. This invention can process TiAl blades of different sizes, including low-pressure turbine blades, high-pressure turbine blades, and axial-flow hollow blades. Blades HIP produced by this method are found to be dense and defect-free by CT inspection, indicating that printing defects are completely eliminated. Because this method utilizes asynchronous temperature and pressure control, leveraging the different microstructural mechanical properties to promote defect closure and annihilation under relatively low temperature and pressure conditions, it solves the problem of internal defects in printed TiAl alloy blades and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of hot isostatic pressing (HIP) technology for engine blades, and in particular to a multi-step HIP method for eliminating defects in TiAl alloy blades using selective electron beam melting. This method is applicable to components such as low-pressure turbine blades, hollow guide vanes, and high-pressure turbine blades using selective electron beam melting. Background Technology

[0002] TiAl alloys possess low density, excellent high-temperature strength, specific strength, and specific modulus, as well as strong oxidation and creep resistance. Compared to nickel-based alloys, TiAl alloys have only half the density, resulting in significant weight reduction. They are currently used in aero-engines and automotive engines. Additive manufacturing is a method for rapidly fabricating complex-shaped TiAl alloy parts. It achieves near-net-shape forming by heating and melting alloy powder layer by layer. Furthermore, electron beam selective melting additive manufacturing features high vacuum and high preheating temperatures, effectively avoiding the effects of oxidation and stress during the printing process. It is currently the most mature method for industrial production of TiAl alloy printed parts.

[0003] The deposition density of TiAl alloy electron beam selective melting additive manufacturing parts typically cannot reach 100%, and defects such as porosity, delamination, and lack of fusion severely affect the mechanical properties of TiAl alloys, especially their fatigue properties. Hot isostatic pressing (HIP) is a processing method that can effectively eliminate defects in casting and additive manufacturing alloys, and it is currently widely used in the post-processing of additive manufacturing.

[0004] Hot isostatic pressing (HIP) can effectively eliminate small-sized defects such as pores. The defect closure process is a process in which microstructures come into contact and connect after creep, ultimately annihilating the defects. However, HIP of TiAl alloys faces a series of challenges: TiAl alloys have high high-temperature strength and good creep resistance in their fully lamellar structure, thus requiring high temperatures and pressures for HIP, currently reaching up to 1290℃ and 230MPa. These excessively high process parameters drastically increase costs. Holding at high processing temperatures can also cause microstructure degradation, and the slow cooling rate of the HIP furnace leads to grain coarsening and an increase in equiaxed γ-grains. Furthermore, high processing temperatures and pressures can cause deformation of components such as blades. These problems have become bottlenecks in the application of HIP technology for TiAl alloy blades.

[0005] For example, Chinese patent CN 116275051 A discloses a TiAl / TC4 alloy laminated composite plate and its preparation method. This method involves hot isostatic pressing of the powder blank. First, it is held at 500–800℃ for 1–2 hours under a pressure of 40–60 MPa. This step aims to achieve bonding and pre-sintering between the powder particles. Then, the temperature is raised to 1250–1350℃ under a pressure of 150–250 MPa and held for 3–5 hours. This step mainly achieves diffusion and bonding between TC4 and TiAl. This method is designed for the sintering, diffusion, and bonding of the powder particles; dense forming relies on the subsequent rolling process. It does not include parameter design for the defect closure of the TiAl alloy.

[0006] Chinese patent CN 111975003 A discloses a method for controlling the full lamellar microstructure of titanium-aluminum alloys. This method involves encapsulating TNM powder in a pure Ti sheath and performing hot isostatic pressing (HIP). The HIP temperature is 1230–1260℃, the pressure is 130–170 MPa, and the holding time is 3–5 h, yielding a TNM alloy sample with a density of 99.98%. However, this method only involves a single HIP step. The excessively high temperature and holding time inevitably lead to grain coarsening, thus reducing the alloy's mechanical properties. Furthermore, a density of 99.98% is not ideal; further improvements would require significantly increasing the pressure and processing time.

[0007] Chinese patent CN 117721346 A discloses a method for preparing SiC fiber-reinforced titanium alloy composite blades. This method involves inserting the composite material into a titanium alloy sheath and a steel sheath, followed by hot isostatic pressing (HIP). The parameters include: temperature: 700–1300℃; pressure: 100–180 MPa; time: 1–10 h. This method uses relatively low temperatures and pressures, primarily achieving bonding between the titanium alloy and SiC fibers, and is not suitable for the HIP of TiAl alloys. Summary of the Invention

[0008] To address the technical problems existing in the hot isostatic pressing process of TiAl alloy electron beam selective additive manufacturing blades, this invention provides a method for fully pressing TiAl alloy electron beam selective additive manufacturing blade defects and adjusting the microstructure at lower pressures and temperatures. The technical solution is as follows:

[0009] A method for eliminating defects in TiAl alloy blades by electron beam selective melting printing using hot isostatic pressing (HIP). The method involves a three-step HIP process after cleaning the blade blank, followed by purging and heating with argon gas to remove air, thus completing the preparation of the TiAl alloy blade. During HIP, the blade is fitted into a tooling fixture to prevent deformation. This method can process TiAl blades of different sizes, including low-pressure turbine blades, high-pressure turbine blades, and axial-flow hollow blades. Before HIP, powder is removed from the support and gaps of the blade blank, and the surface roughness of the blade blank is greater than Ra30, requiring sandblasting.

[0010] Furthermore, before specifying specific parameters, it is necessary to determine the thermophysical properties of the alloy used, such as melting point, Tα point, and lowest phase transformation temperature; after determining the hot isostatic pressing temperature, it is necessary to determine the strength and creep properties of the alloy with a specific microstructure at the relevant temperature.

[0011] Furthermore, in the first step of the process, a vacuum is first applied to 10... -2 Pa, filled with inert gas to 10 -1 Pa, after repeating this process several times, evacuate to 10 Pa. -3 Pa, begin heating and pressurizing; first heat to 1140℃~1240℃, with a heating rate not exceeding 10℃ / minute, and when the temperature reaches 800-900℃, begin pressurizing to 140MPa~150MPa, with a pressurization rate not exceeding 1MPa / minute.

[0012] Furthermore, in the second step of processing, the pressure is first increased to 150MPa~230MPa, with a pressure increase rate not exceeding 0.5MPa / min. After reaching the pressure, the temperature is increased, with a temperature increase rate not exceeding 5℃ / min, and the temperature range is 1250℃~1300℃. The process is carried out until the alloy reaches the Tα point, and then the process is stopped. This process obtains a sufficient number of lamellar structures while compressing defects.

[0013] Furthermore, in the third step of the process, the pressure is kept constant while the temperature is reduced at a rate of not less than 8°C / minute. When the temperature drops below 900°C, the pressure and temperature are gradually reduced to room temperature and atmospheric pressure.

[0014] Furthermore, when the blade length is greater than 50mm, anti-deformation tooling is required. The blade components should maintain a spacing of at least 2cm and should be cleaned before loading into the furnace to prevent surface contamination.

[0015] Furthermore, the tooling can be removed when the temperature inside the furnace drops to room temperature to 100°C. At this time, the temperature inside the tooling is still relatively high. The tooling can be opened and the blades removed only after it has cooled down for several hours.

[0016] Furthermore, the test bar of the hot isostatic pressing blade was dissected to obtain the internal block, which was then made into a metallographic block. After microscopic photography, defects with an internal diameter of less than 50 μm were completely eliminated, while defects larger than 100 μm were difficult to eliminate with hot isostatic pressing.

[0017] Furthermore, after hot isostatic pressing, the blades undergo CT inspection. The voxel size or resolution used needs to be less than 25 μm. After scanning, the portion of the surface extending 0.5 mm inward needs to be removed in the post-processing stage. Similarly, the post-processing results should not contain defects with an equivalent diameter of less than 50 μm.

[0018] The above technical solution has at least the following advantages compared with the existing technology:

[0019] The present invention proposes a multi-step hot isostatic pressing method for eliminating defects in TiAl alloy blades by selective electron beam melting printing. This method addresses the technical problems existing in the hot isostatic pressing process of TiAl alloy blades manufactured by selective electron beam additive manufacturing and provides a method that can fully press together TiAl alloy blades to eliminate defects and adjust the microstructure at lower pressure and temperature, thereby synergistically improving the density and mechanical properties of the electron beam selective additive manufacturing products.

[0020] This invention employs a multi-step heat treatment design, selecting a temperature range within the microstructure where the alloy exhibits strong deformability for pressurization, and then directly cooling down after reaching Tα, thereby ensuring a sufficient number of lamellar structures to meet performance requirements such as fatigue creep.

[0021] This invention, through a multi-step design, can eliminate defects at lower temperatures and pressures, while preventing the degradation of microstructures and deformation of components.

[0022] This invention provides a series of operational methods for cleaning, placing, tooling, and sampling blades through different hot isostatic pressing tests, which are universally applicable to different blades.

[0023] This invention effectively identifies the defect elimination status of blades after hot isostatic pressing by methods such as dissecting metallographic analysis and CT detection, and provides the standard for defect elimination.

[0024] Blades printed using this method via hot isostatic pressing (HIP) were found to be dense and defect-free upon CT inspection, indicating that printing defects were completely eliminated. This method, through asynchronous temperature and pressure control, utilizes the different microstructural mechanical properties to promote defect closure and annihilation under lower temperature and pressure conditions, thus solving the problem of internal defects in printed TiAl alloy blades. Compared to other traditional methods, through parameter design optimization and selection of post-processing and inspection methods, the processed blade components can effectively eliminate defects while retaining good microstructure and mechanical properties. The method is highly applicable, efficient, and conducive to large-scale industrial production and promotion, showing broad application prospects. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a scanning electron microscope image of the microstructure before hot isostatic pressing in Embodiment 1 of the present invention, showing obvious pores;

[0027] Figure 2 This is a scanning electron microscope image of the microstructure after hot isostatic pressing in Example 1 of the present invention. There are no obvious pores, indicating that the pores have healed.

[0028] Figure 3 This is a scanning electron microscope image of the microstructure before hot isostatic pressing in Embodiment 2 of the present invention, showing obvious pores;

[0029] Figure 4 This is a scanning electron microscope image of the microstructure after hot isostatic pressing in Example 2 of the present invention. There are no obvious pores, indicating that the pores have healed.

[0030] Figure 5 The test bar after hot isostatic pressing in Embodiment 3 of the present invention was contaminated by gas and impurities on its surface because no tooling was used for protection.

[0031] Figure 6 The blades in Embodiment 3 of this invention are hot isostatically pressed and protected with tooling. The surface is relatively clean and there is no deformation.

[0032] Figure 7 The blade test bar after hot isostatic pressing in Embodiment 4 of the present invention is protected by tooling, the surface is relatively clean and there is no deformation.

[0033] Figure 8 This is a scanning electron microscope image of the microstructure before hot isostatic pressing in Example 4 of the present invention, showing obvious pores;

[0034] Figure 9 The performance of the blade test bar after hot isostatic pressing in Example 4 of this invention is shown, with a strength reaching 700 MPa. Detailed Implementation

[0035] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0036] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0037] In this embodiment of the invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent. Similarly, the terms "of," "corresponding," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent.

[0038] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0039] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0040] A multi-step hot isostatic pressing method for eliminating defects in TiAl alloy blades via selective electron beam melting printing is disclosed. This method can process TiAl blades of different sizes, including low-pressure turbine blades, high-pressure turbine blades, and axial hollow blades, and includes the following steps.

[0041] (1) Inspect the blade surface. If there is powder in the support or holes and grooves, it needs to be removed first. If the surface roughness of the blade blank is greater than Ra30, it needs to be electrochemically polished or sandblasted.

[0042] (2) Before determining the specific hot isostatic pressing parameters, it is necessary to determine the thermophysical properties of the alloy used, such as the melting point, Tα point, and lowest phase transformation temperature. After determining the hot isostatic pressing temperature, it is necessary to determine the strength and creep properties of the alloy with a specific microstructure at the relevant temperature.

[0043] (3) In the first step of processing, first evacuate to 10 -2 Pa, filled with inert gas to 10 -1 Pa, after repeating this process several times, evacuate to 10 Pa. -3Pa, begin heating and pressurizing. First, heat to the two-phase region of 1140℃~1240℃, with a heating rate not exceeding 10℃ / min. When the temperature reaches the lowest phase transition point of 800-900℃, begin pressurizing to 140MPa~150MPa, with a pressurization rate not exceeding 1MPa / min.

[0044] (4) In the second step of the process, based on the strength of the alloy at the maximum steady-state creep rate at the temperature determined in the first step, the pressure is first increased to 150MPa~230MPa, and the pressure increase rate is no more than 0.5MPa / min. After reaching the pressure, the temperature is increased, and the heating rate is no more than 5℃ / min. The temperature range is 1250℃~1300℃. The process is carried out until the alloy is near the Tα point. After reaching the temperature, the process is stopped. A sufficient number of lamellar structures are obtained while compressing defects.

[0045] (5) During the third step of the process, the pressure is kept constant and the temperature is reduced. The cooling rate is not less than 8°C / minute. The specific cooling rate can be obtained from the CCT curve of the heat treatment of this material. When the temperature drops below 900°C, the pressure and temperature are reduced and gradually reduced to room temperature and atmospheric pressure.

[0046] (6) When the blade length is greater than 50mm, anti-deformation tooling is required, and the blade parts should maintain a spacing of at least 2cm.

[0047] (7) When the temperature inside the furnace drops to room temperature to 100°C, the tooling can be removed. At this time, the temperature inside the tooling is still high. The tooling can be opened and the blades removed after the tooling has cooled down for several hours.

[0048] (8) The test bar of the hot isostatic pressing blade was dissected to obtain the internal block and made into a metallographic block. After observation by microscopic photography, the internal defects with a diameter of less than 50 μm were completely eliminated, while defects with a diameter of more than 100 μm were difficult to eliminate by hot isostatic pressing.

[0049] (9) After hot isostatic pressing, the blade is subjected to CT inspection. The voxel size or resolution used should be less than 25 μm. After scanning, the part of the surface 0.5 mm inward needs to be removed in the post-processing stage. Similarly, there should be no defects with an equivalent diameter of less than 50 μm in the post-processing results.

[0050] The following are specific examples:

[0051] Example 1

[0052] The following steps are included in treating TNM-TiAl blades with a blade height of 70 mm using this method.

[0053] (1) Check the blade surface. The blade support structure has been removed and the surface roughness of the blade blank is less than Ra30.

[0054] (2) The melting point of TNM alloy is about 1600℃, and the processing temperature should be 0.7-0.9 times Tm, i.e., 1120℃-1440℃. The Tα point is about 1240℃, and the lowest phase transformation point is about 850℃. The strength of the bimodal structure is about 600MPa, and the elongation is about 0.8-1.6%. The strength of the fully lamellar structure is about 800MPa, and the elongation is about 0.6-0.8%.

[0055] (3) In the first step of processing, first evacuate to 10 -2 Pa, filled with inert gas to 10 -1 Pa, after repeating this process several times, evacuate to 10 Pa. -3 Pa, begin heating and pressurizing. First, heat to the two-phase region of 1180℃ at a rate of 10℃ / min. When the temperature reaches the lowest phase transition point of 850℃, begin pressurizing to 150MPa at a rate of 1MPa / min.

[0056] (4) In the second step of the process, based on the strength of the alloy at the maximum steady-state creep rate at the temperature determined in the first step, the pressure is first increased to 220 MPa at a rate of 0.5 MPa / min. After reaching the pressure, the temperature is increased at a rate of 5℃ / min until it reaches 1240℃. After reaching the temperature, the process is stopped to obtain a sufficient number of lamellar structures while compressing defects.

[0057] (5) During the third step of the process, the pressure is kept constant and the temperature is reduced at a rate of 8°C / minute. When the temperature drops below 850°C, the pressure and temperature are reduced gradually to room temperature and atmospheric pressure.

[0058] (6) When processing blades with a length of 70mm, anti-deformation tooling is required, and the blade components should be kept at a 3cm gap.

[0059] (7) When the temperature inside the furnace drops to room temperature to 100°C, the tooling can be removed. At this time, the temperature inside the tooling is still high. The tooling can be opened and the blades removed after the tooling has cooled down for several hours.

[0060] (8) The test bar of the hot isostatic pressing blade was dissected to obtain the internal block, which was then made into a metallographic block. The microstructure before hot isostatic pressing was observed by microscopic photography. The scanning electron microscope image of the microstructure before hot isostatic pressing is shown below. Figure 1 As shown, there are obvious pores. The microstructure after hot isostatic pressing is as follows. Figure 2 As shown, the hole has been pressed shut.

[0061] (9) After hot isostatic pressing, the blade is subjected to CT inspection. The voxel size or resolution used should be less than 25 μm. After scanning, the part of the surface 0.5 mm inward needs to be removed in the post-processing stage. Similarly, there should be no defects with an equivalent diameter of less than 50 μm in the post-processing results.

[0062] Example 2

[0063] The following steps are included in treating TNM-TiAl blades with a blade height of 270 mm using this method.

[0064] (1)-(5) are the same as in Example 1.

[0065] (6) When processing blades with a length of 270mm, it is necessary to use extended anti-deformation tooling and maintain a 5cm gap between blade components.

[0066] (7) When the temperature inside the furnace drops to room temperature to 100°C, the tooling can be removed. At this time, the temperature inside the tooling is still high. The tooling can be opened and the blades removed after the tooling has cooled down for several hours.

[0067] (8) The test bar of the hot isostatic pressing blade was dissected to obtain the internal block, which was then made into a metallographic block. The microstructure before hot isostatic pressing was observed by microscopic photography. The scanning electron microscope image of the microstructure before hot isostatic pressing is shown below. Figure 3 As shown, there are obvious pores. The microstructure after hot isostatic pressing is as follows. Figure 4 As shown, the hole has been pressed shut.

[0068] (9) After hot isostatic pressing, the blade is subjected to CT inspection. The voxel size or resolution used should be less than 25 μm. After scanning, the part of the surface 0.5 mm inward needs to be removed in the post-processing stage. Similarly, there should be no defects with an equivalent diameter of less than 50 μm in the post-processing results.

[0069] Example 3

[0070] The following steps are included in treating 4822-TiAl blades with a blade height of 70 mm using this method.

[0071] (1) Check the blade surface. The blade support structure has been removed and the surface roughness of the blade blank is less than Ra30.

[0072] (2) The melting point of alloy 4822 is about 1550℃. The processing temperature should be 0.7-0.9 times Tm, i.e., 1085℃-1395℃. The Tα point is about 1260℃, and the lowest phase transformation point is about 900℃. The strength of the bimodal structure is about 500MPa, and the elongation is about 1.5-3%. The strength of the fully lamellar structure is about 600MPa, and the elongation is about 0.8-1.5%.

[0073] (3) In the first step of processing, first evacuate to 10 -2 Pa, filled with inert gas to 10 -1 Pa, after repeating this process several times, evacuate to 10 Pa. -3 Pa, begin heating and pressurizing. First, heat to the two-phase region of 1260℃ at a rate of 8℃ / min. When the temperature reaches the lowest phase transition point of 900℃, begin pressurizing to 140MPa at a rate of 0.8MPa / min.

[0074] (4) In the second step of the process, based on the strength of the alloy at the maximum steady-state creep rate at the temperature determined in the first step, the pressure is first increased to 200 MPa at a rate of 0.4 MPa / min. After reaching the pressure, the temperature is increased at a rate of 4℃ / min until it reaches 1320℃. After reaching the temperature, the process is stopped to obtain a sufficient number of lamellar structures while compressing defects.

[0075] (5) During the third step of the process, the pressure is kept constant and the temperature is reduced at a rate of 8°C / minute. When the temperature drops below 900°C, the pressure and temperature are reduced gradually to room temperature and atmospheric pressure.

[0076] (6) For blades with a length of 70mm, anti-deformation fixtures are required. The blade components should maintain a 2cm spacing. Test bars not using anti-deformation fixtures should be treated as follows: Figure 5 As shown, the surface is contaminated.

[0077] (7) The tooling can be removed when the internal temperature of the furnace drops to room temperature to 100°C. At this time, the internal temperature of the tooling is still relatively high. The tooling can be opened and the blades removed only after it has cooled down for several hours. Figure 6 As shown.

[0078] (8) The test bar of the hot isostatic pressing blade was dissected to obtain the internal block and made into a metallographic block. After observation by microscopic photography, the internal defects with a diameter of less than 50 μm were completely eliminated, while defects with a diameter of more than 100 μm were difficult to eliminate by hot isostatic pressing.

[0079] (9) After hot isostatic pressing, the blade is subjected to CT inspection. The voxel size or resolution used should be less than 25 μm. After scanning, the part of the surface 0.5 mm inward needs to be removed in the post-processing stage. Similarly, there should be no defects with an equivalent diameter of less than 50 μm in the post-processing results.

[0080] Example 4

[0081] The method for treating high Nb-TiAl blades with a blade height of 270 mm includes the following steps.

[0082] (1) Check the blade surface. The blade support structure has been removed and the surface roughness of the blade blank is less than Ra30.

[0083] (2) The melting point of TNM alloy is about 1650℃, and the processing temperature should be 0.7-0.9 times Tm, i.e., 1155℃-1485℃. The Tα point is about 1290℃, and the lowest phase transformation point is about 900℃. The strength of the bimodal structure is about 750MPa, and the elongation is about 0.5-1.5%. The strength of the fully lamellar structure is about 900MPa, and the elongation is about 0.5-1.0%.

[0084] (3) In the first step of processing, first evacuate to 10 -2 Pa, filled with inert gas to 10 -1 Pa, after repeating this process several times, evacuate to 10 Pa. -3 Pa, begin heating and pressurizing. First, heat to the two-phase region of 1260℃ at a rate of 10℃ / min. When the temperature reaches the lowest phase transition point of 900℃, begin pressurizing to 150MPa at a rate of 1MPa / min.

[0085] (4) In the second step of the process, based on the strength of the alloy at the maximum steady-state creep rate at the temperature determined in the first step, the pressure is first increased to 230 MPa at a rate of 0.5 MPa / min. After reaching the pressure, the temperature is increased at a rate of 5℃ / min until it reaches 1290℃. After reaching the temperature, the process is stopped to obtain a sufficient number of lamellar structures while compressing defects.

[0086] (5) During the third step of the process, the pressure is kept constant and the temperature is reduced at a rate of 8°C / minute. When the temperature drops below 900°C, the pressure and temperature are reduced gradually to room temperature and atmospheric pressure.

[0087] (6) When processing blades with a length of 270mm, it is necessary to use extended anti-deformation tooling and maintain a 3cm gap between blade components.

[0088] (7) The tooling can be removed when the internal temperature of the furnace drops to room temperature to 100°C. At this time, the internal temperature of the tooling is still relatively high. The tooling can be opened and the blades removed only after it has cooled down for several hours. Figure 7 The test bar of the hot isostatic pressing blade shown in the furnace was protected by tooling, the surface was relatively clean, and there was no deformation. Figure 8 The image shows a scanning electron microscope (SEM) image of the microstructure before hot isostatic pressing, revealing obvious pores. Figure 9 The tensile properties of the test bar in the furnace show that it reached a high strength of 700 MPa.

[0089] (8) The test bar of the hot isostatic pressing blade was dissected to obtain the internal block and made into a metallographic block. After observation by microscopic photography, the internal defects with a diameter of less than 50 μm were completely eliminated, while defects with a diameter of more than 100 μm were difficult to eliminate by hot isostatic pressing.

[0090] (9) After hot isostatic pressing, the blade is subjected to CT inspection. The voxel size or resolution used should be less than 25 μm. After scanning, the part of the surface 0.5 mm inward needs to be removed in the post-processing stage. Similarly, there should be no defects with an equivalent diameter of less than 50 μm in the post-processing results.

[0091] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0092] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0093] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0094] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for eliminating defects in TiAl alloy blades by selective electron beam melting and hot isostatic pressing, characterized in that, After the printed blade blank is cleaned, the air is discharged by circulating argon gas and then heated and pressurized to carry out a three-step hot isostatic pressing process to complete the preparation of TiAl alloy blades. During hot isostatic pressing, the blade blank is placed into a tooling to prevent deformation. The method can process TiAl alloy blades of different sizes. Before hot isostatic pressing, the powder in the support and gaps of the blank is removed. When the surface roughness of the blade blank is greater than Ra30, sandblasting is performed. The three-step thermo-isostatic pressing process, which involves purging air by cyclically filling and releasing argon gas followed by heating and pressurization, is as follows: In the first step of the process, a vacuum is first drawn to 10. -2 Pa, argon gas was introduced to 10 -1 Pa, after repeating this process several times, evacuate to 10 Pa. -3 Pa, start heating and pressurizing; first heat up to 1140℃~1240℃, heating rate not greater than 10℃ / min, when the temperature reaches 800-900℃ start pressurizing to 140MPa~150MPa, pressurizing rate not greater than 1MPa / min. In the second step of processing, the pressure is first increased to 150MPa~230MPa, and the pressure increase rate is no more than 0.5MPa / min. After reaching the pressure, the temperature is increased, and the temperature increase rate is no more than 5℃ / min. The temperature is increased to Tα, so as to obtain a sufficient number of lamellar structures while compressing defects. In the third step of the process, after the temperature reaches Tα, it is directly cooled down while maintaining constant pressure. The cooling rate is not less than 8℃ / minute. When the temperature drops below 900℃, the pressure and temperature are gradually reduced to room temperature and atmospheric pressure.

2. The method for eliminating defects by electron beam selective melting printing of TiAl alloy blades using hot isostatic pressing according to claim 1, characterized in that, Before determining specific parameters, it is necessary to determine the melting point, Tα point, and minimum phase transformation temperature of the alloy used; after determining the hot isostatic pressing temperature, it is necessary to determine the strength and creep properties of the alloy with a specific microstructure at the relevant temperature.

3. The method for eliminating defects in TiAl alloy blades by selective electron beam melting printing and hot isostatic pressing according to claim 1, characterized in that, TiAl alloy blades of different sizes are used for low-pressure turbine blades, high-pressure turbine blades, and axial flow hollow blades.

4. The method for eliminating defects by electron beam selective melting printing of TiAl alloy blades using hot isostatic pressing according to claim 1, characterized in that, When the temperature inside the furnace drops to room temperature to 100°C, the tooling is removed. At this time, the temperature inside the tooling is still relatively high. The tooling can be opened and the blades removed only after it has cooled down for several hours.

5. The method for eliminating defects by electron beam selective melting printing of TiAl alloy blades using hot isostatic pressing according to claim 1, characterized in that, The test bar of the hot isostatic pressing blade was dissected to obtain the internal block, which was then made into a metallographic block. After microscopic photography, the internal defects with a diameter of less than 50 μm were completely eliminated, while defects with a diameter of more than 100 μm were difficult to eliminate by hot isostatic pressing.

6. The method for eliminating defects by electron beam selective melting printing of TiAl alloy blades using hot isostatic pressing according to claim 1, characterized in that, The blades were subjected to CT inspection after hot isostatic pressing. The voxel size used was less than 25μm. After printing, the portion 0.5mm from the surface to the inside was removed during the hot isostatic pressing stage.

Images